Dithieno[3,2-b:2′,3′-d]pyrrol-Cored Hole Transport Material Enabling Over 21% Efficiency Dopant-Free Perovskite Solar Cells

Dopant-free hole transport materials (HTMs) are essential for commercialization of perovskite solar cells (PSCs). However, power conversion efficiencies (PCEs) of the state-of-the-art PSCs with small molecule dopant-free HTMs are below 20%. Herein, a simple dithieno[3,2-b:2 ',3 '-d]pyrrol-cored small molecule, DTP-C6Th, is reported as a promising dopant-free HTM. Compared with commonly used spiro-OMeTAD, DTP-C6Th exhibits a similar energy level, a better hole mobility of 4.18 x 10(-4) cm(2) V-1 s(-1), and more efficient hole extraction, enabling efficient and stable PSCs with a dopant-free HTM. With the addition of an ultrathin poly(methyl methacrylate) passivation layer and properly tuning the composition of the perovskite absorber layer, a champion PCE of 21.04% is achieved, which is the highest value for small molecule dopant-free HTM based PSCs to date. Additionally, PSCs using the DTP-C6Th HTM exhibit significantly improved long-term stability compared with the conventional cells with the metal additive doped spiro-OMeTAD HTM. Therefore, this work provides a new candidate and effective device engineering strategy for achieving high PCEs with dopant-free HTMs.